System of controlling energization to thermal head in thermal printer

Abstract

An energization control system for controlling energization of a thermal head of a thermal printer, the thermal head being equipped with a plurality of heating elements successively arranged in line, which are energized to generate heat in response to supply of currents thereinto so as to thermally and gradationally print an image on a recording sheet with printing densities corresponding to the supplied currents. The system comprises a density correction data memory for storing density correction data corresponding to variations of resistances of the heating elements and a calculation circuit for correcting an image signal on the basis of the density correction data so as to produce image data. Also included is a data comparison circuit selectively coupled through a switching device to the density correction data memory and the calculation circuit for comparing first and second comparison signals with the density correction data and the image data. The data comparison circuit performs first energization so as to energize the heating elements in accordance with the comparison result between the first comparison signal and the density correction data and, after completion of the first energization, performs second energization so as to energize them in accordance with the comparison result between the second comparison signal and the image data.

What is claimed is: 
     
       1. An energization control system for controlling energization of a thermal head of a thermal printer, said thermal head being equipped with a plurality of heating elements successively arranged in line, said elements being energized to generate heat in response to sufficient currents being supplied thereto so as to thermally and gradationally print an image on a recording sheet with printing densities corresponding to the supplied currents, said energization control system comprising: inputting means for inputting an image signal whereby said thermal printer prints said image on said recording sheet through said thermal head;   density correction data memory means for storing density correction data corresponding to variations of resistances of said heating elements;   calculation circuit means coupled to said inputting means and said density correction data memory means for correcting the inputted image signal on the basis of said density correction data so as to produce image data;   level counter means arranged to act as an up-counter and a down-counter for generating first and second comparison signals; and   data comparison means coupled to said level counter means and further selectively coupled through switching means to said density correction data memory means and the calculation circuit means for comparing said first and second comparison signals with said density correction data from said density correction data memory means and said image data from said calculation circuit means, said data comparison means performing first energization so as to energize said heating elements of said thermal head in accordance with a comparison result between said first comparison signal and said density correction data and, after completion of said first energization, performing second energization so as to energize said heating elements thereof in accordance with a comparison result between said second comparison signal and said image data.   
     
     
       2. An energization control system as claimed in claim 1, wherein said level counter means acts as the down-counter during said first energization and acts as the up-counter during said second energization. 
     
     
       3. An energization control system as claimed in claim 1, wherein said switching means is arranged so as to effect a switching operation so that said data comparison means is coupled to said calculation means for performing said second energization after elapse of a predetermined time period from the completion of said first energization.